Fresh water tank cleaning

Trying to clean the freasy water tank in my KK42.
It's very rank. Doing the chlorine bleach thing and rinsing. Any tips?
Thanks in advance

Let it sit for a bit, and if you can take the boat for a ride even better, slosh the bleach around, also if you have them, clean your strainers, they get pretty nasty also.

Can you get to the top of the tank? I put the tanks in my ride and put deck hatches on top. Remove the hatches and you can clean it out with a mop/shopvac/whatever.

Sometimes it's hard to think outside the box. Yes I can get to the top and there is room to cut a large opening. Goes against my nature to cut factory stuff but in this case it might be an improvement. Great idea thank you

What year KK42? Our water tanks (2-150 gallon each), has a ~6-8” ss inspection port on the top of the rear section of the tank. Ours is under the hanging locker’s floor in the guest stateroom. Once a year I empty the tanks and take a high velocity nozzle on a garden hose, blast the inside, drain and repeat till they look clean. Other than that, we haven’t done or do anything else in 12 years. We do filter all the water that goes into the tanks other than from the water maker. We also live on and cruise full time so the water gets turned over regularly.

If you put bleach in your tanks, make sure to run the faucets and shower until you can smell the bleach, Then let it set for 24-48 hours, then rinse several times. Good to go.

Additive-free bleach is great for tank cleaning. Hot water is good.


UV light is used for tank disinfecting.


A local health dept, extension service, or water company might have guidelines.


Assuming freasy is greasy: A food safe surfactant is worth a look. Enzymes and surfactants are effective together.

My boat is a 1980. It has a single 400 gallon molded tank, same location as yours. Unless there is an access port on the engine room side hiding, there doesn't seem to be one.

Take a look at a product called Puriclean. Practical Sailor Magazine did extensive testing of tank cleaning products and methods. This was their top choice. It not only killed the biofilm on the tank walls, it caused it to fall off so it could be flushed from the tank.
Clean Tabs Ltd | Water Purification | Water Purification Tablets | Water Tank Cleaning | Water Treatment | Drinking Water Disinfection

I'll check it out. Thank you

My 42 also has an access port for the port tank under the steps.