Some models have no in-tank fuel pump but a strainer. This is a passive filter to avoid debris going into the pump

This is from a 1987 298S4 model

The sieve is part number 928.201.081.04

The torque value is 25 Nm (18.4 ft lb). From WSM 20-14 (describing the in tank pump replacement for Japan models).

I wasn't able to find any other mention of the pump or strainer in the WSM or the tech notes. It's probably buried in there somewhere, I just couldn't find it.

The 924S has the exact same bung for an in-tank pump/strainer (in fact, the strainer part # is the same on the 928 and 924S). On page 20-2b of the WSM for the 924S, it says that the torque is 36 to 44 Nm (26 to 32 ft lb).

I went with the smaller value (25 Nm) when I replaced my in tank pump with a strainer on my '87 928 several years ago and haven't had any leaking at all. When I replaced the strainer on my 1987 924S, I used the same 25 Nm and it has also been leak free. It's easy to tighten up further if needed, so I like to start with the lighter value first.

The manuals all state to use a brand new gasket anytime you install an in tank pump/strainer, which I think plays a big role in making a good seal.