Cleaning out my tank

[brew]

I have an 81 gs450 that sat for a couple of years before i got it. After running for about 100 miles it started giving me problems so i pulled the carbs and they were full of crap. So i cleaned those and decided to empty the tank and clean that out while it was off the bike. The gas was just strait brown coming out of it, so i emptied it out and rinsed it with water really good but there is still alot of sediment in the bottom. Is there any way to get that out. Even with flipping the tank over not all the water will come out, and the fuel switch will not coming off at all so i dont know how to drain it fully. Also, after rinsing it with water, it got a surface rust within a few minutes of being emptied, any words of advice for that?
Thanks in advance,
Brew

[Blueandorangefish]

Maybe try penetrating oil on the bolts to the stuck screws.

As someone dealing with a similar problem right now, I would suggest just taking it to a radiator shop and letting them dip it in acid then seal it.

[Nessism]

There are several different tank cleaning/sealing products on the market. Por-15 is quite popular. Do a search for more info.

[tkent02]

Remove the petcock so you don't damage the screens, make a plate to block the hole. Same with the gas gauge if you have one. Put a gallon of Kerosene and a bunch of BBs in and shake the **** out of it for as long as you can. Especially slop the stuff up and down the bottom of the tank, that's where most of the rust is. The tank won't rust afterwards, most of the rust will come out. Shouldn't need to seal it unless you are going to let it sit for months at a time.

You will still need an inline filter perhaps if you don't get all the rust out, but that's no big deal if you get the right kind, made for bikes.

[almarconi]

Remove the petcock and any other parts attached to the tank. Seal up the holes with some sheet metal plates. Fill the tank up about 1/2-3/4 full with water and add phosphoric acid. Let the acid sit in the tank for about a day. Periodically shake the tank and then let it sit. The acid will dissolve the rust and leave a phosphate coating on the clean metal. Carefully dump out the acid. Remove the plates. If you have a pressure washer, thoroughly clean the inside of the tank to remove all the acid and residual rust. You can use a mixture of baking soda and water to neutralize any residual acid. After removing as much water as possible, I like to dump in about a cup of acetone to remove any residual water. You can then spray some WD40 in the tank or put a light coating of oil on the metal to protect against flash rust.
If the rust is really bad and you have pin holes you will need to seal the tank. There are many products available for this POR-15, Caswell epoxy..etc.
Another method that works well is electrolysis. Do a search on this site, there are several threads that explain how this process works.