Can you use the same mana ability twice in one mana pool filling without spells in between?

Mana abilities are special: they don't use the stack and can be activated any time you have priority (or are asked to pay a cost). There is no rule preventing you from activating the same mana ability multiple times in a row to accumulate mana in your mana pool before spending it. This follows from CR 605.3a, which simply states that mana abilities resolve immediately and their mana is added to your pool.

Your mana pool persists within a step or phase until you spend it or the phase ends (CR 106.4). So you can tap a land, float one mana, then activate a mana-producing creature ability, then tap another land — all before casting a single spell — and all that mana sits in your pool ready to use.

The same source can be used repeatedly as long as you can pay its cost each time. For example, if you control a Llanowar Elves (tap: add G), you can only tap it once per turn since it becomes tapped. But an untapped artifact that says '{T}: Add {C}' can only be tapped once too. However, a repeatable ability like '{1}: Add {C}' on Krark-Clan Ironworks (or similar) can be activated as many times as you can pay {1}, back-to-back, generating multiple mana before you spend any of it.

Concrete example: You control Gilded Lotus ({T}: Add three mana of any one color). You tap it for {U}{U}{U}. You cannot tap it again this turn (it's now tapped), but separately, you also control Nirkana Revenant (whenever you tap a Swamp for mana, add {B} on top). After tapping two Swamps, you have {B}{B}{B}{B} plus the {U}{U}{U} — all accumulated without casting anything in between.

In summary, CR 605.3a and CR 106.4 together confirm there is no restriction on activating the same or different mana abilities multiple times consecutively to fill your mana pool before spending it.