It's a Machlokes (matter of dispute):
"...One can be lenient in regard to the halachos that apply.
However, most poskim argue....
 Refer to Eretz Tzvi 1:110:-111:pages 375-378, Maharam Brisk 3:39,
Masef Lechul Hamachanus 4:96, Zekan Aaron 1:1, Edos L’Yisroel page
113:1, Chelkes Yaakov 1:205, Minchas Yitzchok 1:60, Yechaveh Da’as
3:1, Ohr L’tyzion 1:1, 2:1:9, Shearim Metzuyanim B’Halacha 1:2:6,
Sharei Ha’beracha 1:footnote 122 in depth.
 Masef Lechul Hamachanus 4:96, 43:5, Har Tzvi O.C. 1:50, Chazzon
Ish O.C. 17:4, Igros Moshe E.H. 1:114, Shraga Hameir 3:26, Halichos
Shlomo Tefilla 20:24, Yabea Omer 3:2, Teshuvos V’hanhugos 1:4, Be’er
Moshe 4:3:9, Rivevos Ephraim 7:1, 8:583, Divrei Chachumim page
20:footnote 5, Avnei Yushfei 1:5:1, Kedushas Hamachanei
K’hilchosa9:6:footnote 14. A room which is only made for urinals is
still considered a bathroom (Mishnah Berurah 83:12)..."
The later-day poskim dispute whether our bathrooms have the halachic
status of the beis hakisei of the days of Chazal. Some poskim are
lenient since our bathrooms are much cleaner than old-time outhouses
(Shu’t Zakan Aharon 1:1; Shu’t Minchas Yitzchok 1:60). Others contend
that our bathrooms should still be treated as a beis hakisei (see
Shu’t Yechaveh Daas 3:1). Both the Chazon Ish (Orach Chayim 17:4) and
Rav Moshe Feinstein (Shu’t Igros Moshe, Even HaEzer 1:114) rule that
we should treat our bathrooms as a safek (questionable) beis hakisei.
The universal practice is to not recite brachos in the bathroom, but
some people are lenient to wash their hands there. Rav Moshe rules
that one may not wash for bread in our bathrooms, but one may wash his
hands there before davening, although one should dry one’s hands
outside the bathroom.
"...In addition, Rav Shlomo Zalman Auerbach (cited in Mikra’ei Kodesh,
Yom Kippur, p. 157, note 17) stated that there is no need today to be
particular for halachos of ruach ra’ah that are not mentioned in the
Gemara. Although he was referring to the halachah of walking 4 amos
before netillas yadayim in the morning, the same can be applied here,
with regard to netilas yadayim after entering a bathroom.
Because of these factors, some poskim write that one can actually wash
netillas yadayim in a bathroom, though several write that where
possible, it is better not to do this.
See: Chazon Ish, Orach Chaim 17:4; Minchas Yitzchak 1:60 (explaining
why it is permitted, but concluding that one should not be lenient
under ordinary circumstances); Beis Shlomo 18; Levush Mordechai 182;
Eretz Tzvi 110"
For more, see:
Your Camp Shall Be Holy: Halacha And Modern Plumbing” inThe Journal of Halacha and Contemporary Society, (spring 1995): 29:89-128