Gray Tank vs Black Tank Dumping Water Flow Speed

[jadams]

Hello All...

Heading out for our 6th trip since we were first able to camp on July 4th weekend. Happy to have a few more planned into early November. I've been wondering about this.

Every time I dump the tanks I notice the black water comes out at high speed, like a torrent. The hose moves a little side to side because of the water pressure. When I open the gray tank the water comes out at about a 1/3 of the pressure. This is with both tanks almost full to full.

17B parked level to angled towards the dump receptacle (if dump station parking pad is sloped). Black valve closed before opening gray valve. I definitely have the the gray valve fully opened.

Only water, soap and oral hygiene products go into the gray tank.

I have insulation under the 17 B so I'm not able to see the tanks and angle of the pipes.

Funny thing, emptying the black tank is very satisfying for me because of the high pressure and quickness of the dump. The gray tank is disappointing in comparison, it's too slow.

[Centex]

One factor contributing to your observations is the 'elevation head' difference between the two tanks (the pressure relating to the difference in elevation between the liquid in the tank and the outlet).

Noting that the black tank located above the trailer floor is higher (directly under the toilet pedestal and relatively tall profile) than the grey tank located below the trailer floor and with a much lower profile.

Those differences are meaningful in this context, they're inherent ('fixed'), and the resulting observed pressure / flow-rate difference is not indicative of a problem.

Not gonna touch the satisfaction factor!

[Dave Walter]

My experience with the black and gray is the same. Black empties quickly within a few seconds and with a "whoosh". The gray takes its time and seems to take forever to stop dripping. Seems to help if I drive the door side wheels of the Escape on a wooden block before dumping, but is still generally quite slow.

[rubicon327]

Some of us have upsized the gray line to 2" but the primary benefit was getting the valves facing forward (which I believe ETI does now anyway). This helps a little bit but the big difference in dumping speed versus black is how the tanks are situated as mentioned earlier. Try pulling up on a wood block on the opposite side. Also the venting could be slowing it down. Try it with the shower drain stop valve open. The gray will never be as quick as the black but you may find ways to gain an incremental improvement.

[padlin]

If you look at the tanks the outlet for the black is 3" I think and underneath, so you get a great flow. The grey is outlet is something like 1.5" and mounted at the bottom of the side of the tank, not underneath. I had measured once and when the grey's flow slows way down there is less then 3 gallons left so you've gotten 90% out. When traveling I no longer wait for the trickle to stop.

[arniesea]

Originally Posted by jadams

Hello All...

Funny thing, emptying the black tank is very satisfying for me because of the high pressure and quickness of the dump. The gray tank is disappointing in comparison, it's too slow.

As others have mentioned, the relative head pressure due to tank hight and pipe diameter are the reason.

As to satisfaction, I agree with your assessment. So my strategy when at a campground with full hookups is to empty the tanks before doing any other task related to breaking camp. I watch that black tank empty with satisfaction, close it, then open the grey tank valve and walk away. I try to do as many other tasks before returning to finish up. (Note: I leave the city water connected so I can use my "outdoor shower" tap with hose to rinse out my stinky slinky before putting it all away.)

At a dump station there is often a line, so I don't bother emptying the grey fully. When planning a long trip, I tend to look for a campground with full hookups the last night before retuning home.

Cheers!

[CoolCampingKid]

The height of the tanks is a factor but also the size of the pipes are different as well. No comment on satisfaction but I do like empty holding tanks!

[jadams]

Thank you for taking the time to reply everyone.

The different tank placement in the trailer, location of the outlets on the holding tanks and different pipe diameters make sense. It's good to hear different outflow rates is normal.

Arnie & Paula- I like your gray tank draining strategy and keeping city water line hooked-up when at a campsite with hook-ups. I also like elevating the passenger side wheel mentioned a few times.

Good to hear some of you enjoy emptying holding tanks also!

[cpaharley2008]

Just be careful with having the trailer hooked up to water and and then leaving it unattended. Some units have have been flooded. You may want to turn off the o/s faucet to release any pressure inside.