Canned tuna: pour off the lake without sieve
If you open a tuna preserve with brine, the water must drip off. I proceed as follows:
Open the can with the ring pull closure. Then hold the can diagonally down over the sink and press in the lid. The water is dripping off now.
In principle, that also works with tuna in oil. I warn against pouring this into the drain because the oil gets stuck in the drain pipes. I put the oil in a twist-off glass, which I dispose of in the Altglascontainer. The oil burns in the molten glass.