I was a bit careless with my test stand setup, using only filtering in the supply tank (paper pleat filter). In no time carb problems raised their head and I had to clean the internal carb filter.
In my plane, the carb filter stays clean, because I use one on board filter filter in the fill line, and a felt clunk filter in the fuel pickup.
Two put an additional filter in the fuel pickup line seems overkill, because there is no way any debris can enter that line between tank and carb. (no T-connections)