6x12mm silicone tube is what was included with my main pump. I'm also using some of that for the same purpose. It's very stiff, but I inserted a bent large paperclip to force it to bend the right angle when stored on the top of the tank.
Block diagrams for power wiring below. I don't know how much sense it makes to anyone else. You may have to download the full size version to read anything.
https://i.imgur.com/THFX3gU.png <-full size
One of the most important thing to plan out with a complicated electronics setup is the negative/ground wiring. I have frequently had to rethink and review the diagrams to avoid ground loops or accidentally sending motor currents through signal wires. I've tried as much as possible to send all ground paths in a star pattern back to central points closely connected to the battery.
For example, one critical point is the signal path that sends the SBUS signal from the receiver to the Arduino mega. To ensure that the difference between ground and signal voltage is the same at both places, one might usually directly connect the ground between the two components, but that's risky when they have different power sources. For the final design the signal goes from receiver to esp32 to arduino mega. The ground path goes back to the ESC, through the battery wires to the central distribution board and then to the arduino mega. Including a ground wire with the signal wire could send several amps of servo current through the ground traces on the arduino mega itself, or even motor currents, at best raising the voltage on the ground traces, at worst burning the arduino.
I still feel doing a master battery switch was correct, but now I would have placed a switch on the "drive" branch too, so I could disconnect the motor while testing. A switch on the pump seemed like a good idea to avoid water accidents and the idea behind the switch on the electronics branch was so I could disconnect it while developing the arduino stuff. Of course with the arduino stuff mostly done long before the truck was driveable, that switch is quite useless now.