I don't believe it was capable of it, which is why it was so massive. The SR-71, which required inflight refueling repeatedly, only held 80k pounds of fuel (about 12k gallons). I don't have any good sense of fuel burn vs speed either, but in general, jets like to run high and fast. The old Lear 23s burned about as much fuel (pounds per hour) idling on the ground as they did at cruise, and I think the SR-71 (which mostly used the turbojets to keep the afterburners lit, at cruise...) fuel economy up high was quite good. Apparently the major problem with performance was keeping it from overspeeding - left to their own devices, the engine (... entire engine assembly, however long it was) was running so efficiently that they just wanted to go.
The actually built XB-70's- the two prototypes- did not have a refueling receptacle. Production models would have had a boom receptacle just like the B-47, B-52 and B-58 did. It would have gone in the upper fuselage about where the delta wing starts.
