blackwater tank sediment

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New member
Apr 4, 2005
NW Arkansas
I need a little help from all you seasoned rv folks. I recently bought a Holiday Rambler 5th wheel used. I initially thought the blackwater tank gauge sending unit was bad. It was, in fact reading right. Someone had left the tank partially filled and it has about 1/2 to 2/3 of a tank of sediment in it. I purchased some enzymes from a local rv store to add to the tank as soon as the weather gets warm, but am a little  skeptical as to wether this will work. Has anyone had this problem; and how did they fix it. Other than this problem, I LOVE the camper and I got a really good deal, so I can't complain about a little maintenance. Any tips would be greatly appreciated.

Steve CDN

Well-known member
Jan 31, 2005
Congratulations on your new rig, and Welcom to the RV Forum.  We're glad you found us, where we enjoy meeting new RVing friends.  Feel free to join in any ongoing discussion, or start one of your own.

Because the message discussions in our Forum are threaded, which means replies are glued to the previous message in the discussion, you would not want to post the same query in more than one message section.  Doing so confuses potential responders and fragments the discussion and you lose valuable insights.

Luckily the Volunteer Forum Staff can usually manage any duplicate postings to help get the most impact to your query.

It sounds like the previous owner may have left the dump valve open while parked for a prolonged period, causing a build up of solid sludge at the bottom of the black tank.

Pour a couple of bags of ice cubes into the toilet, and add several gallons of water with baking soda.

Then drive the coach several miles, preferably on a bumpy road to slosh around and break up the sludge.  Try dumping the contents.  If ansecond application is required, try hot water instead.

Perhaps othe Forum members may have other methods that have worked for them.

Kepp us posted on your progress.


Moderator Emeritus
Jan 29, 2005
Home is where we park it
Welcome to the RV Forum Framily.  Congratulations on the new to you Holiday Rambler.  Steve has given you sme very good suggestions.  It may require preforming the steps Steve mentione several time to get it cleaned out.  Some dealers use a steam cleaner to clean the holding tank on units traded in.  I would try Steves suggestions first.

Gary RV_Wizard

Site Team
Feb 2, 2005
West Palm Beach, FL
Are you sure your tank is 1/2 - 2/3 full of sediment? Or is it just that the gauge is reading in that range?  The latter is much more likely.  The sending units in the tank work by passing a tiny electrical current between electrodes set into the side of the tank at differnt levels. If crap collects on them they give false readings, a very common problem with this sort of gauge.  I would soak the tank thoroughly (at least a day, more is better) by filling and adding your enzymes.  Then try Steve's ice cube trick, which can rub offcaked on crud.  Then repeat the enzyme soak.  It may take several cycles.  A good detergent might work as well as the enzyme stuff, especially if what the dealer gave you is a standard enzyme based holding tank chemical. Those aren't really made for cleaning caked on crud - they are for routine addition to your tank in every day use.

A web search on "enzyme tank cleaner"( without the quotes) will turn up a number of enzyme CLEANER products if you want something heavy duty.
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