Does return line have check valve in the tank?
 

I have 120-PSI fuel pressure in the fuel distributor on my 280SL Euro and found out that the restriction was in the return fuel line. Checked return line from the fuel distributor to the tank and is OK, but the problem is in the tank. Does the return line in the tank end with a check valve and if this is the case how to clean it? When I cleaned the tank I, blew air thru the return line connection and some air were passing under the pressure.

Thanks for any help.