Why would any one in there right mind use water to flush out the tank in the
van? Let alone at any time. There are numerous solvents that you can use that
are much better. Alcohol for one.
Disconnect the fuel line, open filler cap and let gravity do the work. Then
take said crudy fuel and filter it with some paint filters. Replace into tank
and repeat till clear.
Add new in line filter when you reconnect the fuel line. I have done this
several times with old beetles and cars that have sat for years, and it has
always worked.

Jim Morgan 86GL
"Breadbox" 205,000.0
Westlake,Ohio