Hanging cargo on a string?

We are going to attend a drone competition where we are supposed to make an autonomous firefighting drone. We were caught between storing the water in a rigidly attached tank and using a pump to fill it up vs. using a bucket tied to a string like the ones similar to irl firefighting helis. We are planning on a 3 kg dry mass with 5 kg water capacity. The obvious downside of the bucket is the large mass that can swing from side to side. How big of a concern is this? Can it be a significant enough factor to crash the drone? Won’t the sloshing water in a rigidly attached tank cause a similar issue? If both of these are a bad idea, what can be a better solution? Thanks in advance.

I haven’t tried that much weight but smaller payloads work well hanging from a tether.
The copter and the payload work together and it is good to watch.
Search for videos, they are around somewhere…

Is 3kg dry mass the mass of the aircraft and 5kg water capacity the mass of the payload?

Might be. Depending on the payload.

Not as much as the first case but yes.

The tank should be as close as to the CoG (vertical and lateral). Also, inside the tank, there should be some walls that dampen waves. Any payloads that are not rigidly attached to the copter are potential disturbances.

A similar use case is hanging a magnetometer on a cable from the drone for abandoned oil well detection. Multirotors handle that well enough.

That’s called a slingload.
I’ve flown with 20 something kilos of it.
World fine, but for fast deceleration from high speed, a RC pilot can do it nicer than the autopilot.
It won’t crash anything that flies well.

Thanks a lot everyone!