For a true gravity x-feed between wing tanks and all pumps inop try this:
1. Establish stable flight on desired course and at assigned FL.
(1-A. Suspend cabin beverage service if relevant.)
2. Apply substantial trim sufficient to bank about 30 degrees, heavy wing high. Re-trim as needed to maintain course and altitude.
3. Level wings periodically to recheck fuel balance.
4. Consult OPS/Dispatch as necessary, possibly preparing to land a bit early for repairs, and...
5. Rinse and Repeat as necessary.
