Radially attached 3 fuel tanks but only one is connected to engine.
I connected 3 fuel tanks with symmetry around lander can.
At bottom of lander can is spark engine.
dV is calculated for 1 fuel tank draining only.
Only one fuel tank drains when spark engine is used.
When that tank is empty, engine will stop.
I can still refill that tank manually with fuel transfer from other 2 tanks.