I honestly don't like liquiducts that much. In order to pull liquids you need a redstone signal, which means one more block needed (as opposed to an autarchic gate on the pipe itself), and in one case already the signal was activating something it shouldn't (I almost blew up an IC transformer). You also can't connect two machines directly with only one liquiduct, you need to have at least one input and one output piece - where you only need one wooden water pipe. The extra throughput might be worth it in rare cases (steam boilers and such), but in almost any case pipes are fast enough and much more compact.
For the OP's issue, add more valves to the tank and pump lava by several pipes/liquiducts simultaneously. I'd also like to know how are you getting it in the tank in the first place, if pipes don't have enough throughput? Multiple pumps attached directly to the tank or something?