Drop 3-5 drops after filling. If there is residual ink, gently hang the nib on the ink bottle mouth. Then, with the tip of the pen facing up, carefully blot the ink left on the tip and tongue with a paper towel (blot it, not dry it, so be careful, because the paper towel fiber can easily enter the pen seam). This method is suitable for people who only write a few words (signatures or something) a day. If you write a lot, it doesn't matter if you drop one tube of ink or erase one tube of ink a day.
And remember not to touch the bottom of the bottle when filling water. It's not because @ Liu Jia said that "carbon ink will corrode pens" (will it actually corrode? It is because carbon ink will block the pen.