[Gthywdeagle]

1999 Mariah 4.3l inboard. Cranks and runs but stalls out when applying throttle. Removed filter. Had a lot of trash. Did run fine when started for first time. However ran out of gas. Has alum tank. Had bugs and other thrash in filter. Looks I need to clean out tank but not sure how to do this. Clean lines, etc.

[ColoradoDiablo]

Welcome to MOC!
Your going to have to drain and clean through the fill inlet.
Take fill hose off at tank inlet and run a siphon hose in the tank and out the bilge drain hole. Takes awhile , but it is the easiest way. Unless you have a electric pump laying around.
Just be very careful working with the fuel. Make sure you are outside and keep all spark of any kind away!