I have a kurbmaster van and it hade a bt-4 cummins in it and swicthed it to a 300cid and wondering what to do about the fuel tank and the diesel that is sill in the tank or the residue that the diesel has left behind. I'm wondering what is the best way to clean the tank out. thank you

 

Drain it, remove it and rinse it with gas.

 

i would do what ARCTICY BLOCK said. i had a 1986 that had a 6.9 diesel in it and i put a 400 in. i dropped the tanks and empty the diesel out and gave that away then i took gas and poured in the gas tank slushed it around a few times and dumped it out and repeated like 1 or 2 times then after that go ahead and make sure the vent valve on the tank is not clogged and works right if not replace it and replace the vent tubing. this will save frustration when you go to pump gas. i have not had any problems with my tabks since i started to run gas in them.
nother thing to look at when you drop the gas tanks most of the time the screens on the pick up tub is rotted and in sevarl pieces. i could not find anyone thats sold new screens for the pick up so i took like and inch or inch and half gas hose and added it to the pick up tube so you can get most of the gas out of the tank. other wise there will always be like 5 gals or so you will never use. i just run the in line fuel filters to caught all the dirt i might be sucking up. one on each tank and one before the carb. hope this answers any questions and makes your day a little easy after its done. i done dropped my tanks a few times for stupid reasons, that if i done it all the first time i would have to kept dropping them.