For the distance it's really just the same than other weapons: practice.
I like playing the sloshing as it's really fun. But as I said in other threads I believe the weapon is just a bit weaker than others, so you wouldn't see it in competitive (or very rarely).
For instance, from my point of view, it's pretty strong on Skatepark. My thinking is that the map allows short and middle range to get in their distance quite easily, and it's the single best weapon to kill people hiding on the snipe. It's better than blasters because obviously, gravity. But the problem is, luna is even stronger on this map. And that's like this in every map I thought of. Each time I think "oh, sloshing should be good on this", I then think "but if it's true then this weapon (a blaster mainly) will be even better".
I believe it's because blasters have a very consistent 2HKO. I mean, what is more scary: playing a good sloshin' user who will splat you in 2-3 shots consistently, or fighting a good luna who will splat you in a faster 2HKO and some 1HKO, and has the respawn-jump option? The second is (at least) viable on any map, and will still be viable on maps where the sloshing machine is good...
Though well, as with any weapon, when the player is good it's still scary.
Stuffs I saw so far:
- lots of damage up ("easy way" I guess), I wouldn't recommend it.
- lots of defense up (quite interesting)
I personanly tried:
- ink stuff, allowing more bomb combo (I liked it)
- special stuff with some bomb range, cause splat rush is still very strong and it gives some more power to the user I feel, but still prefer the more balance ink option
About ink efficiency, depending on how much you use the bombs, it can be a real problem.
Maps I believe the sloshing machine is interesting: Blackbelly, Bluefin.
There are others I have in mind but well, even on these two, a blaster in easier. And being easier will give more options (especially powerplays). About bluefin, it's because the weapon is good at killing people in the two mid fights.