Thetford 875 porta potti with MSD

SounderSolutions · Posted: Mon Jan 26, 2015 8:59 pm Post subject: Thetford 875 porta potti with MSD

I am having a problem getting the pump out function of this toilet to work. The first attempt failed because I could not plug the overboard vent line which prevented me from getting a vacuum. I had my 'ahh moment' when I realized what the tube and cap under the sink is for.

I installed the tube and cap which blocks the over board vent. Thinking I should be able to get a vacuum, I tried again. No luck. I put water on top of the flush valve to see if there was a leak. Sure enough, the water gets pulled into the toilet which results in no vaccuum.

Am I missing something? The manual does not provide ANY info about the MSD procedure. Do I need to seperate the top and bottom? Is there a way to seal or 'referesh' the seal on the flush valve? Any help will be appreciated as this thing needs to get emptied SOON.

Thanks,
Steve

Bill K · Posted: Mon Jan 26, 2015 9:47 pm Post subject:

You do NOT make a vacuum on the tank, just the pumpout hose.

I would say that either that hose and fittings has a leak or your not drawing from the bottom of the tank.

If you close the vent line and get the other problem fixed you will collapses the holding tank.

Bill Kelleher

Aurelia · Posted: Mon Jan 26, 2015 10:07 pm Post subject:

Correct, don't plug anything at all. Just hook up (hold tight) the vacuum pumpout hose and keep the flush flap closed so you don't get any splashes where you don't want them. If you are not getting anything, you have....

-A significant air leak between pumpout fitting and portapotti
-Too low a level of waste in the tank for the MSD fitting to pickup (does not fully empty the tank)
-No way for air to flow in while you are sucking air/waste out, don't block the vent line

After pumping out, run a couple gallons of freshwater back into the pumpout fitting and then suck it back out. We did that a couple of times each pumpout and it kept the unit much fresher.

Greg

SounderSolutions · Posted: Mon Jan 26, 2015 11:58 pm Post subject:

Thank you for the quick feedback. My next course of action sounds like i need to fill it up with freshwater and try again. Fortunately there is only liquid in there right now.

So keep the vent tube on and unobstructed? Then what the heck is that tube under the sink for??? Lol

Steve

Aurelia · Posted: Tue Jan 27, 2015 12:13 am Post subject:

Not sure which tube you are referring to. The MSD fitting should have two parts, a large outlet, and a smaller vent. Is your vent line terminating under your sink? If so, you should really move it outside with a simple throug-hull fitting or something similar. Do you have bathroom odors in the under-sink area?

Greg

Bill K · Posted: Tue Jan 27, 2015 12:29 am Post subject:

Here is link to a parts list, it may help.

I could not find a manual for the 875.

http://www.thetford.com/HOME/PARTS/PortableToilets/AquaMate875PartsNEW/tabid/641/Default.aspx

Bill Kelleher

SounderSolutions · Posted: Tue Jan 27, 2015 12:51 am Post subject:

Lollygaggin · Posted: Sat Jan 31, 2015 1:53 pm Post subject:

If your vent line got plugged somehow, as in wasp nest etc, you might experience the same problem with pumping out. Try opening the flush valve just a wee bit to be sure there is air flow "in" while the vacuum is applied. We also found that the rubber adaptor on the end of the pump out hose had to be pushed in really hard to make a good seal. We have to tie the boat as close and tight to the dock as we can get it and then literally lean on the hose end to get the seal needed to make the pump out work. This is not to say that I'm a "pump out" expert here 'cause we've only ever used one pump out location and it may be totally different with the set up you are trying to use. Good luck.

Bill K · Posted: Sat Jan 31, 2015 2:12 pm Post subject:

Another trick is to run water around the vacuum hose connection at the boat to help seal it.

Bill Kelleher