Fresh Water Tank Vacuum System - Escape Trailer Owners Community

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Old 03-26-2016, 04:47 PM   #1
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Fresh Water Tank Vacuum System

This is the fourth of five links that address my efforts to clean, and keep clean, my 17 footer fresh water tank.

This is the first link. http://www.escapeforum.org/forums/f8/fresh-water-tank-extreme-maintenance-7425.html#post134332

This is the next link. http://www.escapeforum.org/forums/f8/fresh-water-tank-cover-7429.html#post134336

While scrubbing the inside of my fresh water tank as discussed in this other post, TBD I was very surprised to see a lot of water remaining after the tank was completely drained via the standard drain cock, which is not the low point of the tank. A shallow pool of water extended over more than 1/3 of the tank bottom. I later determined that there was approximately 1.9 gallons of trapped water in the tank. No wonder I had cooties growing in the tank, it is a pretty good hydroponic greenhouse; lots of light, humid and wet.

I wanted to totally drain the fresh water tank and if possible dry it, but the obvious options were not acceptable, they were:

1. Spin-weld a new fitting on the bottom of the tank to provide a proper low point drain. Unfortunately our local RV service center can’t do spin welding and the nearest other service centers were at least 60 miles away. I didn’t check to see if they could do spin welding. Plus I was a little concerned about adding a new fitting to the bottom of a 10 year old tank.

2. Glue on a new low point drain. Unfortunately an adhesively bonded fitting would not hold as the low density polyethylene (LDPE) plastic that I assume the tank is made from is impervious to most chemicals and glue will not effectively stick.

3. Use an expandable rubber plug inserted into a hole drilled in the bottom of the tank. I thought this may make the water taste odd and the tank thickness (1/8th inch) may not be adequate to hold the plug without possibly cracking of the plastic.

This led me to make a vacuum system to remove the trapped water in the tank. In addition to removing the trapped water, I could also use the vacuum to more effectively dry the tank by removing standing water and puddles throughout the tank. I figured I could also use the system to scrub cooties from the interior surface and remove them if they appear in the future.

The vacuum works very well and is fun to use. It takes 10 to 15 minutes to thoroughly vacuum and almost dry the tank. I removed approximately 1.9 gallons of water by taking off the drain cock and using the vacuum system.

The main problem of course is access to the inside of the tank…

The system gains access to the inside of the tank through the existing drain cock fitting. This fitting is plastic or nylon and has pretty sloppy threads. It is also easily cross threaded.

I replaced the drain cock with a new PVC drain fitting shown on the first picture. This will protect the threads in the tank as I will only have to remove the threaded cap to access the tank. To keep the PVC riser from rotating in the fresh water tank inlet threads when I tried to take of the cap, I added an electrical conduit jam nut (to keep the riser from rotating) and a hose clamp (to give me something to hold on to as I rotated the cap. The PVC pipe fitting protects the tank threads and prevents me from accidently cross threading the drain cock if I was to reinstall it. I think it would be pretty easy to damage the water tank threads with repeated removal and reinstallation of the drain cock.

The vacuum system is shown on the second picture. It is a four foot long clear plastic hose with a steel fitting on one end and PVC fittings glued on with silicone on the other.

I insert the end with the steel fitting into the tank and hook the other end of the plastic hose up to a wet/dry shop vac. I turn on the shop vac and maneuver the steel fitting and hose around the tank with a strong magnet (salvaged from a computer hard drive) held up to the outside of the tank. The steel fitting is large enough that I can see it through the plastic tank material. I move the fitting and hose around the tank until I am satisfied I have done enough and keep an eye on the clear tube to see when water is no longer being pulled out before moving to a new area. It is pretty fun and I can vacuum the tank in 10 or 15 minutes.

I actually made two systems with different ends as shown on the third picture. The magnet is also show. The knurled end can be used to scrub local areas of the tank. The smooth end is what I will normally use. The end pieces are pneumatic tool male plugs with the wrench hex heads ground off. These are similar. http://www.amazon.com/Milton-S-1809-Male-Plug-P-Style/dp/B000COS0MY/ref=sr_1_sc_2?ie=UTF8&qid=1459020182&sr=8-2-spell&keywords=pnuematic+tool+male+automotive+fitt ing I had to grind of the hex heads to get the fittings into the tank.

I will use the vacuum system every time we go camping. I will wipe it down to sterilize it before I put it in the tank. It should take about 10 minutes to dry the tank. I have the high lift axle so there is adequate space to work.

For those interested in how I determined the amount of water trapped, here are the details.

After draining the fresh water tank via the drain cock, I removed the drain cock and drained approximately 77 ounces of trapped water into a container. This is approximately 2.4 quarts or 2.3 liters.

I then used the vacuum and removed an additional 162 ounces of trapped water. This is approximately 5.1 quarts or 4.8 liters. Altogether I drained approximately 239 ounces or 7.5 quarts or 7.1 liters or trapped water, this is approximately 1.9 gallons of water. This is almost 10% of the rated capacity of the tank.
Attached Images
File Type: jpg New Drain.jpg (261.0 KB, 14 views)
File Type: jpg Vacuum.jpg (272.9 KB, 11 views)
File Type: jpg Both ends.jpg (190.6 KB, 12 views)
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Old 03-26-2016, 06:10 PM   #2
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Quote:
Originally Posted by Thane View Post
1. Spin-weld a new fitting on the bottom of the tank to provide a proper low point drain. Unfortunately our local RV service center can’t do spin welding and the nearest other service centers were at least 60 miles away. I didn’t check to see if they could do spin welding. Plus I was a little concerned about adding a new fitting to the bottom of a 10 year old tank.
That seems like a promising approach. Maybe someone else will try it.

I've never spin-welded anything, but my understanding is that the only special equipment that is required is a drive fitting; people do it at home (perhaps with a borrowed drive fitting, if they're only doing it a couple of times). It seems strange that the local RV service centre doesn't have experience with it - perhaps they're one of those places that just replaces parts and doesn't actually fix or modify anything.

I understand the concern about age, but LDPE is still a thermoplastic at any age - it will still melt.

Quote:
Originally Posted by Thane View Post
3. Use an expandable rubber plug inserted into a hole drilled in the bottom of the tank. I thought this may make the water taste odd and the tank thickness (1/8th inch) may not be adequate to hold the plug without possibly cracking of the plastic.
Aside from the rubber and thickness/stress issue, the plug would protrude into the interior and still leave an undrained dead space.
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Old 03-26-2016, 06:26 PM   #3
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Great work, excellent instruction.
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Old 03-26-2016, 07:46 PM   #4
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Thanks for the replies. The local shop said they didn't have the spin welding high speed tool and experienced employee anymore and they haven't had anyone ask for this sort of repair for many years. It's a small shop in a small town but I heard they do good work. I'd probably goof it up if I tried it...
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Old 03-26-2016, 09:15 PM   #5
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The local shop said they didn't have the spin welding high speed tool and experienced employee anymore and they haven't had anyone ask for this sort of repair for many years.
That makes sense. I suppose not many people custom-build or modify RVs - if they want another feature they just park the old one somewhere and buy a whole new trailer.

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I'd probably goof it up if I tried it...
I wouldn't try it before several practice runs on an old tank from a salvage yard.
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