Liquid Fuel-only tanks. Options?

[AgincourtDB]

So I'm 700+hrs and I'm only now finally getting to the point where I'm planning on sending Kerbalnauts to other planets. I'd like to design a Nuclear mid-stage based on the 2.5m engine but off course there's no tank option. My heavy tug for dragging things around in Kerbin orbit uses it with fuel lines coming in from tanks mounted radially, but I'd like a more elegant solution (also, it has 16 separate tanks and that's a PITA to refuel manually). I'd also like to design LF dumps that don't use the oddly-shaped Mk3 tanks but still hold a lot of fuel.

I've tried IFS but it doesn't seem to work, doesn't give me the option of changing the fuel loadout on tanks, just seems to have added a bunch of cryo tanks (??). 

Halp!

I guess ideally I'd like a recommendation for a parts pack that has several LF options of various sizes.Thanks!

[MaximumThrust]

It's not a good ideia to add new parts just for this, they occupy space in the parts list and increases the load times. This can make a huge difference when using a ton of mods.

I think the best way is with Modular Fuel Tanks. With it you can chance the contents of LF/Ox/MP/Xenon of any tank, stock or from mods. It's really simple and useful.

 

[DStaal]

There are several fuel-switcher mods around - probably the most flexible (and therefore the most complex) is Configurable Containers:

 

[AgincourtDB]

Thanks folks! Will try these.

[FleshJeb]

In addition to the other great info here, you should check out TAC Fuel Balancer. I wouldn't play KSP without it.

Very easy, when you're hooked up to a fuel dump, to just set a few big tanks on the dump to "Out".

[Tyko]

another option: