Why does GD recommend opening black tank valve during flush?

[TustinGuy]

Just curious. Why is the recommendation that we keep the black tank valve open while flushing the tank "clean"? Is it purely so we don't forget that we are filling the black tank with water? If one stands there and counts 20 or 30 seconds (with the black tank valve closed), wouldn't that be fine? I would think we could clean the tank better by filling it more. Or is there a technical reason to keep that valve open? (Thanks in advance. I did search for this in the forum and didn't see it asked before.)

[StephenO]

Just curious. Why is the recommendation that we keep the black tank valve open while flushing the tank "clean"? Is it purely so we don't forget that we are filling the black tank with water? If one stands there and counts 20 or 30 seconds (with the black tank valve closed), wouldn't that be fine? I would think we could clean the tank better by filling it more. Or is there a technical reason to keep that valve open? (Thanks in advance. I did search for this in the forum and didn't see it asked before.)

While this technically isn't your first post, I'll still say "Welcome!", and if you hadn't had a chance to check out the welcome letter for new members, please check it out!

To answer your question about leaving the valve open, you're exactly right. You don't want to leave it running and then have your black tank overflow. Obviously that would make your trip awful. Many members here, myself included, will initially dump the black tank, close the valve and turn on the rinse allowing it to fill will clean(er) water again and then dump that. I believe most will allow the black tank to fill while they are dumping the grey water. If you do that though, you'll want to give your sewer hose a really good rinse when done, since you'll be running 'black'-ish water through the hose after the grey. Usually you use the grey water dump to help rinse.

What you don't want to do, is leave a hose connected all the time to your black tank rinse connection, relying on a single valve to stop water from entering the tank. If that valve fails and you don't notice....well, you know.

Again, welcome!

[TustinGuy]

Thanks Stephen! I kinda figured this since the black tank has a venting pipe and couldn't see a good reason for it. (Other than the mess of having it come back up.) And yes, I tend to just deal with the black tank first (including multiple opens) before I open the gray pipes - but thank you for mentioning that in case others don't think about that. I'm glad to know I'm not going to blow out anything by rinsing that way.

[TustinGuy]

Deleting this question since I just figured it out.

[TucsonJim]

I've seen several reports of owners flushing their tanks with the valve closed and after a while, they get a brown geyser coming out of the vent when they get distracted. With that said, here's how I do it. I set an alarm on my phone for 3 minutes. Then I close the valve and let it partially fill. After 3 minutes, I open the valve and let it dump. Then repeat the process 3-4 times. Once the discharge is running clean, I shut off the water and disconnect.

Jim

[JBill9694]

A reliable in-line flow meter can be added to the flush hose and then the black tank filled to say 2/3rds of its rated capacity regardless of the water supply pressure (which relates to flow). Setting an alarm is an excellent idea.

[Guest]

Just curious. Why is the recommendation that we keep the black tank valve open while flushing the tank "clean"? Is it purely so we don't forget that we are filling the black tank with water? If one stands there and counts 20 or 30 seconds (with the black tank valve closed), wouldn't that be fine? I would think we could clean the tank better by filling it more. Or is there a technical reason to keep that valve open? (Thanks in advance. I did search for this in the forum and didn't see it asked before.)

I do this to better clean the black tank but as stated by folks above, if you forget to open the valve, it will be extremely unpleasant. I close my valve for up to a minute and when I open the valve, additional waste will be removed.

Jim

[Jkwilson]

I don’t take my hand off the black tank valve while the flush is running. Too easy to get distracted if you even look away.

[Jlawles2]

For tank flushing what I have found works for getting the chunks out of the bottom is to open the black and let it completely drain, then shut off the gate at the hose (i added the Valterra) and open the gray's, count 30 sec or so, then close the grey's and re-open the hose gate. I do this several times. Then I go for the tank flush port, this time I close the black valve and monitor my water meter opening the valve at the 5-7 gallon mark. let drain, repeat, let drain, repeat, then drain grey tanks and put 5-7 gallons of clear water in the black for the initial loading for use.

Let me credit Rob and a few others (if I try to name the I will miss a few) for the pre loading the tank with a known volume of water.

[Ebkent62]

I use these LCD water meters on both my city water hose and my black tank rinse hose to monitor usage/fill. They’ve been pretty accurate so far. Bought one in white (use on city water hose) and one green (use on black water rinse hose) so I don’t cross contaminate. And as a backup, I set a timer on my Fitbit (watch) to remind me to check the number of gallons that have gone in the black tank. About $18 on Amazon and I think I got mine a little cheaper last year on Walmart.com. Here’s a link for them on Amazon….

Save a Drop Easy-to-Read LCD Water Meter
by Timers Plus
Learn more: https://www.amazon.com/dp/B00D8GT3YM...S0TR05KSAJ5KHH

[Country Campers]

To add to this and the water meter usage. I use the water meter for most things water related especially for filling the black tank after use, yes I said filling. I put about 10 gallons in the black tank thru the black tank flush line to help keep the tank clean, sloshing while traveling, and also as a "starter" for the next trip. I believe this is another Rob, Cate&Rob , suggestion. The reason for the "starter" is so there is ample amount of water in the tank to help dissolve the solids. Trying to get enough water in the black tank from the toilet is hard to do, we have tried.

Brian

[tortuga]

if you don't disconnect the flush water supply hose and there is a hard freeze you may take out your backflow preventer and have a lot of water in hard to remove places the next time you try to flush

[ThePowells]

I cut my vent pipe about 6 inches above the tank top, installed a high water alarm and used the rubber sleeve to reseal the vent pipe.