Sorry for the late answer.
The simplest way is to make 2 or 3 small tanks (you will need 50 dT of fuel). No need to make them droppable or to alter the ship.
The tanks should be built at 100D from where you will be getting fuel & will stay there until you jump away. This way you won't have the accelerate or enter an atmosphere with the tanks attached. This way no need to make anything fancy to attach the tanks (won't need to hold acceleration).
1st jump will be 1 parsec, with 250dT & requires 25dT of fuel. Both tanks stay attached.
After the jump, the ship will be in deep space. Transfer 25dT to the ship inner tanks & drop (throw away) the empty tank.
2nd jump will be 1 parsec, with 225dT & requires 22.5dT of fuel. The remaining tanks stays attached.
After the jump, the ship will still be in deep space. Transfer 25dT to the ship inner tanks & drop (throw away) the empty tank. This will top the jump fuel with some leftover for powerplant.
3rd jump can be a 2 parsec jump toward the nearest system. It will just need 40dT of fuel.
This way, no need to bother with the TL of the tanks, you won't drop them just before the jump -> No jump penalty. And the construction will be simplified, just a pair of tanks capable of holding LHyd with a way to transfert the fuel (might be a pump in the hold, no need to put it in a disposable tank).