1. go scuba diving in eilat you will see subs that are not ther
The good thing about submarines is they can stay underwater so they can swim around the coast in Eilat if they want and then return to Haifa.
Israel is also within its rights to reverse this policy as Eilat it Israeli territory.
It is also a policy that may very well change within the next 3-4 years as the submarine fleet expands from 3 - 5 which would in theory allow Israel to keep at least 1 sub further out and another to defend Israels borders.
There is no way that Israel would have spent over $1 billion to buy an extra 2 submarines if it already had 3 and their only use was going to be to patrol Israeli borders.
Israel has grander ambitions for its submarine fleet.
Also when there are 5 subs to maintain it might just be decided more facilities are needed and there will be a new faciility opened in Eilat which officially is a maintenance dock but in reality a base.
2. I don't think they'll keep an expensive sub in Red Sea
It's too dangerous to keep the sub within the reach of the Egyptian fleet for a long time. Besides, there could be sabotage from third party special forces coming from Egypt's territory - we all know Egyptian government doesn't control the Sinai fully.