After I received the expensive glass cup, I suddenly felt if I used it, I would feel pain/it would be a pain. After I received the expensive glass cup, I suddenly felt if I used it, I would feel pain/it would be a pain.

You would feel pain? How so? Or do you mean it would be a pain? As in a struggle to use. Not sure what you meant here, my apologies

My teacups, part 4. My teacups, part 4.

Considering that I already hadve a few teacups, I gave the tea-water separation teacup to my former leader, who helped me a lot when I was young. Considering that I already have a few teacups, I gave the tea-water separation teacup to my former leader, who helped me a lot when I was young.

Three of them are in my office, while one of them is in myat home. Three of them are in my office, while one of them is at home.

Prepositions - at/in/on Usually, we say things and people are at home rather than in. Also, no need to say 'my home' because you are talking from a 1st person's perspective :3 just home will do

TheI bought a cheap one that was 300 ml and with a stainless steel filter inside of the opening of the cup, and the other expensive one was aone was an expensive type of tea-water separation cup. I bought a cheap one that was 300ml with a stainless steel filter inside of the opening of the cup, and the other one was an expensive type of tea-water separation cup.

You didn't clarify before that you were purchasing a cheap one and an expensive so better to clarify beforehand or do it here. "The other expensive one", implies as though you have two expensive cups, instead of just one.

Inside the lower half of the teacup, there was an isolation valve and peopleyou could open or close the valve through revolving the bottom lid to separate or connect the water and the tea leaves. Inside the lower half of the teacup, there was an isolation valve and you could open or close the valve through revolving the bottom lid to separate or connect the water and the tea leaves.

I think it would sound better to say 'you' instead of people, as you're just talking in general to the reader.

In the meantime, I thought I should have foufind a filter for my first insulation teacup on the internet and. I regretted very much for not thinking of this idea before I bought the second insulation cup with a filter. In the meantime, I thought I should find a filter for my first insulation teacup on the internet. I regret not thinking of this before I bought the second insulation cup with a filter.

You are talking about something you want to do in the future so use future tense - I should find "I regretted very much for not thinking of this idea", sounds unnatural. Usually, people would say "I regret..." And so forth

When I received it, I immediately put it into the opening of my first insulation cup and it fitted the cup so well. When I received it, I immediately put it into the opening of my first insulation cup and it fitted the cup well.

"So well" is a bit more of an informal register compared to the rest of your text. "Well" alone is more formal and suits your formal register here

The tip was thatechnique was after you poureding the boiling water into your cup, please don't cover your cup lid, except thatup the lid, otherwise, the water would become cold. The technique was after pouring the boiling water into your cup, don't cover up the lid, otherwise, the water would become cold.

"Tip" - is usually used when someone gave you a tip or you're giving someone a tip. I would use "technique" instead "Please" is unneeded here as well You clarified it was a cup before so you can just use 'lid' alone

Presently, I wdon't need to buy more teacups because I already have four cups. Presently, I don't need to buy more teacups because I already have four.

You expressed in the first word that this is set in the present - so use the present tense - I do not No need to repeat 'cup' as well