I would note that I believe the use of the post-communion ablution cup can be legitimated within the rubrics of the IGMR (GIRM). However, the principle the person above cited is absolutely factually incorrect.
This was explicitly rejected by dubia. While the dubia was related to incensation, it answers more generally precisely what altarman asserted.
In Notitae 14 (1978) 301-302, no. 2 reads:
DUBIA: In Mass with a congregation celebrated more solemnly, different ways of incensation are being used: one plain and simple; the other, the same as the rite for incensation prescribed in the former Roman Missal. Which usage should be followed?
REPLY: It must never be forgotten that the Missal of Pope Paul VI has, since 1970, supplanted the one called improperly “the Missal of St. Pius V,” and completely so, in both texts and rubrics. When the rubrics of the Missal of Paul VI say nothing or say little on particulars in some places, it is not to be inferred that the former rite should be observed. Therefore, the multiple and complex gestures for incensation as prescribed in the former Missal (see , Vatican Polyglot Press, 1962: VIII and pp. LXXXLXXXIII) are not to be resumed
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In incensation the celebrant (GIRM nos. 51 and 105) proceeds as follows: a. toward the gifts: he incenses with three swings, as the deacon does toward the Book of the Gospels; b. toward the cross: he incenses with three swings when he comes in front of it; c. toward the altar: he incenses continuously from the side as he passes around the altar, making no distinction between the altar table and the base.