Work's fine with SW1 and SW2.
Can LED's be added so that visually I can see that the low or high probes are active?

Try this arrangement.

 

Here is what happens with LED addtion wired up.

Probes out of water. Pump is off, OK. LED2 comes on dimly.
Put lower probe in. Pump does not go on, OK. LED2 goes brighter.
Lower and upper probe in. Pump is on. LED1, 2 & 3 are on. Looks good.
Remove upper probe, lower still in water. LED1, 2 & 3 are all still on.
Both probes out of water, pump stops. LED1 & 3 off, LED2 is still on.

Power cycle.
Probes out of water. Pump is off. LED2 goes on.
Press the momentary switch SW2. Pump goes on. LED1 & 3 go on. When the momentary switch is off LED3 goes dim slowly like the discharge of a cap.

Power cycle.
When I used the trabmitter/receiver/servo, SW1. The same happens as the momentary switch.

 

Add 100K resistors from the base to ground on Q2 and Q3.
Check diode D5.