Attack of the Blob!

[BrentB]

I know there are many threads about how to sanitize tanks, and I have done that, but I still have a problem. While using my water pump, water would flow ok for a while, then slow to a trickle and stay there. I finally discovered that the pump filter was clogged with algae. I cleaned the filter, but the same thing happened again, so I decided to take a look in the tank and the result is what you see in the photo.

This gunk is not fazed by bleach, even at 200 ppm, and is too big to drain through the tiny 3/8 inch drain hole. I would love to scrape and scrub the inside of the tank to get rid of it, but of course the problem is gaining access. My first thought was some kind of access port, but I am having difficulty finding something that I think would work.
I found this, but it seems too small: https://www.marinesan.com/Holding-Ta.../307238685.htm

I found this, but it seems too large: http://www.hendersons.co.uk/boattank/Tank-access.html

And I’m not sure if either will withstand the pressure of being submerged. (There is no access to the tank from above.)

I also thought of installing a larger drain fitting, hoping that the gunk will drain out, but I see that the spin weld fittings require a router, not a drill, and I don’t want to buy one of those. The only access to the tank is from the bottom or one end and the tank is about 4-5 feet long.

I just ran across this, not sure if it would work to build a larger drain: https://www.usplastic.com/catalog/it...x?itemid=89951

I really want to clean the gunk out without removing the tank as that is not easy to do.

Does anyone have any other solutions that I haven’t thought of?

[Suite Sweets]

google How to Get Rid of Algae. You'll find a utube video and a number of products to kill algae. Once it's dead, I think with time, it will break apart, and can be drained out of your tank drain. Maybe others can provide better leads

[John Landry]

I think that you can find a hole saw to use with a drill to make the size hole for the first or second access port hole. You can also check with a marine store and find something to kill the algae. You will probably need a steam cleaner pressure washer to clean the tank after algae is killed.