This is for boats with black water holding tanks.

The smell is probably caused by permeated sanitation hose.  The cause of this is urine and waste which are acidic. This over time penetrates the hose and produces a pungent odor. It most likely will not smell like sewage. It actually has a burn the nostrils smell. What you smell is the acid.  There is an easy test to see if yours are permeated. Using a clean rag go down in the hull of the boat and locate the black water holding tanks. Note, they are usually on the same side the pump outs are on. Using the rag rub it back and forth on the upper hose coming into the tank. Yep you got it, "smell the rag". If you get an odor off the rag the hoses need to be replaced.

Don't panic, its not really that bad or hard to do. First you need to identify all the hose in the system. Using a tape measure determine how many feet you will need.  Remember the bottom hoses coming off the tank. These are your pump out hoses. They will need replacing as well.  Most likely your boat has 1½" diameter hose in it.  This is NOT regular old hose. It has to be replaced with good quality sanitation hose. I will tell you where to get it and clamps at the end of this article. 

After you get all that's needed to do the job you will need to flush each head 4 or 5 times to wash out the hoses. Then get pumped out completely.   If you choose you can add a gallon of bleach in each tank through the pump out ports. NOT IN THE TOILET. Then finish filling with a garden hose through the pump out ports. Discard the hose after use. Have the tanks pumped out again after this. 

Now we are ready to replace all the hoses. First go down in the hull and locate the lake water stand pipes supplying your pumps for each head. There should be a shut off valve on each one. Shut them off. Re-flush each head to empty the bowls.

Locate and remove the bolts holding the head to the floor. Rotate the head around so you can see the hoses coming to it. Take the clamps loose at each connection. Note it may take a sharp razor knife to slice the hose for easy removal.   Just slice it from the end down towards the hose about two inches. This will allow the hose to expand away from the connector and make easy removal. This will be done at each connection.

Go down in the hull and carefully pull the old hose down through the floor. At this time remove the other end from the top connection on the holding tank. Remove the rest of the hoses in the same manner. Note; On the pump out hoses you will need to remove the clamps at the tank and then go outside and remove the screws holding the pump out ports to the side of your boat. Pull it out so you can get to these clamps.

Now we are ready to install the new hoses. You will do this by measuring the old hoses and cutting your new ones to length. Re install in the same sequence you removed them. Remember to slide you new clamps on the hose first. Use cooking oil to lube the attaching hose about two inches in. This will make the hose easier to slide onto the connector. Tighten the clamps tight but not so tight as to deform the hose. Make certain that the hose does not sag anywhere because this can cause waste to sit in the hose like a water trap. 

Turn the lake water stand valves back on and flush each head several times. Check for leaks at this time.  If all is well reposition the heads and bolt them back down.

You should be ready to go and be odor free for 5 more years.

If you flush the head once you will clear the waste from the bowl. If you flush the head twice you will clear the waste from the hose. If you flush the head three times after use you will run clean water through the hose. Three flushes means three times more water in the holding tanks but will ensure no waste will sit in the hose. You be the judge. It is always a good idea to be pumped out after each boating use. You don't have to have full tanks to be pumped out. Uncle Ricky says it's as simple as that.