Great tip! I do the same thing when I'm not using a pump sprayer at very low pressure with the nozzle twisted to "mist".
i like mustard squeeze bottles because they have smaller openings.
But ketchup bottles are bigger and hold more water.
Your idea of actually buying a condiment bottle would never have occurred to me, but I bet the tiny tip is great for this purpose.
Sometimes I give the bottle a small down-and-up shake so that just a little "plop" of water comes out in one cell.
Sometimes I squeeze a continuous thin stream while I move the bottle along a row.
To be extra-gentle, I'll squirt the continuous stream onto the plastic dividers between rows. Then the water runs off the divider and into the mix with no force.
